正颌截骨术中的凸柱体网格切割算法研究

计算机辅助虚拟手术技术对正颌外科手术方案的制定、手术效果的预测分析发挥着重要作用。然而,现有的计算机辅助正颌截骨术只能实现少量简单的截骨操作,不能满足虚拟截骨术多样性的需要。在平面切割地基础上,提出了一种基于凸柱体网格切割算法。该算法用凸柱体模拟虚拟手术刀对三维网格模型进行切割,根据截骨术的切口类型构造柱体,用此柱体进行切割实现骨块的分离。实验结果表明,该算法能有效地实现多种复杂虚拟截骨术,为手术方案的制订提供了辅助指导作用。     

A comparative evaluation of foreground/background sketch-based mesh segmentation algorithms

This paper presents an extensive comparative evaluation of five popular foreground/background sketch-based interactive mesh segmentation algorithms, addressing the quantitative assessment of the accuracy, efficiency, and stability of each algorithm. To facilitate the comparison, we have developed a complete framework with an intuitive and simple sketch-based interface to enable interactive mesh segmentation by marking strokes to specify the foreground and background with the mouse buttons, allowing us to quantify the algorithms in a unified manner. The evaluation has been performed via extensive user experiments in which each participant was assigned to segment models with the evaluated algorithms and the corresponding update of each segmentation was recorded as a new refinement when additional interactions were added. We then collected the segmentations from participants and evaluated them against the ground-truth corpus constructed from the Princeton segmentation database. To investigate how well the interactive segmentations match the ground-truth, five metrics were used to measure the boundary and region accuracy of segmentations. By studying the experimental results, we have analyzed the performance of the evaluated algorithms and provided valuable insights into their characteristics.     

Multivariate density estimation: A comparative study

This paper is a continuation of the authors' earlier work [1], where a version of the Tråvén's [2] Gaussian clustering neural network (being a recursive counterpart of the EM algorithm) has been investigated. A comparative simulation study of the Gaussian clustering algorithm [1], two versions of plug-in kernel estimators and a version of Friedman's projection pursuit algorithm are presented for two- and three-dimensional data. Simulations show that the projection pursuit algorithm is a good or a very good estimator, provided, however, that the number of projections is suitably chosen. Although practically confined to estimating normal mixtures, the simulations confirm general reliability of plug-in estimators, and show the same property of the Gaussian clustering algorithm. Indeed, the simulations confirm the earlier conjecture that this last estimator proivdes a way of effectively estimating arbitrary and highly structured continuous densities on R^d, at least for small d, either by using this estimator itself or, rather, by using it as a pilot estimator for a newly proposed plug-in estimator.     

Robust interactive cutting based on an adaptive octree simulation mesh

We present an adaptive octree based approach for interactive cutting of deformable objects. Our technique relies on efficient refine- and node split-operations. These are sufficient to robustly represent cuts in the mechanical simulation mesh. A high-resolution surface embedded into the octree is employed to represent a cut visually. Model modification is performed in the rest state of the object, which is accomplished by back-transformation of the blade geometry. This results in an improved robustness of our approach. Further, an efficient update of the correspondences between simulation elements and surface vertices is proposed. The robustness and efficiency of our approach is underlined in test examples as well as by integrating it into a prototype surgical simulator.     

Revolute manipulator workspace optimization: A comparative study

Robotic manipulators with three revolute families of positional configurations are very common in the industrial robots. The capability of a robot largely depends on the workspace of the manipulator apart from other parameters. In this work, an evolutionary optimization algorithm based on foraging behavior of Escherichia coli bacteria present in human intestine is utilized to optimize the workspace volume of a 3R manipulator. The proposed optimization method is subjected to some modifications for faster convergence than the original algorithm. Further, the method is also very useful in optimization problems in a highly constrained environment such as the robot workspace optimization. The test results are compared with standard results available using other optimization algorithms such as Differential Evolution, Genetic Algorithm and Particle Swarm Optimization. In addition, this work extends the application of the proposed algorithm to two different industrial robots. An important implication of this paper is that the present algorithm is found to be superior to other methods in terms of computational efficiency.     

Semi-supervised model-based document clustering: A comparative study

Semi-supervised learning has become an attractive methodology for improving classification models and is often viewed as using unlabeled data to aid supervised learning. However, it can also be viewed as using labeled data to help clustering, namely, semi-supervised clustering. Viewing semi-supervised learning from a clustering angle is useful in practical situations when the set of labels available in labeled data are not complete, i.e., unlabeled data contain new classes that are not present in labeled data. This paper analyzes several multinomial model-based semi-supervised document clustering methods under a principled model-based clustering framework. The framework naturally leads to a deterministic annealing extension of existing semi-supervised clustering approaches. We compare three (slightly) different semi-supervised approaches for clustering documents: Seeded damnl, Constrained damnl, and Feedback-based damnl, where damnl stands for multinomial model-based deterministic annealing algorithm. The first two are extensions of the seeded k-means and constrained k-means algorithms studied by Basu et al. (2002); the last one is motivated by Cohn et al. (2003). Through empirical experiments on text datasets, we show that: (a) deterministic annealing can often significantly improve the performance of semi-supervised clustering; (b) the constrained approach is the best when available labels are complete whereas the feedback-based approach excels when available labels are incomplete. Editor: Andrew Moore     

Ethical implications of internet monitoring: A comparative study

Organizations have become increasingly concerned about employee use of the Internet for personal reasons while at work. Monitoring Internet usage has become more and more prevalent in the workplace. While there may be legitimate business functions such as employee performance appraisal that are served by monitoring, poorly designed and communicated monitoring practices can have negative effects on employee morale and may be considered an invasion of privacy. Universities are another venue where Internet monitoring occurs. This paper explores whether there was a significant difference in attitude towards Internet usage and monitoring at the university as compared to the workplace. It is the result of a comparative study.     

A survey of interactive mesh‐cutting techniques and a new method for implementing generalized interactive mesh cutting using virtual tools‡

In our experience, mesh‐cutting methods can be distinguished by how their solutions address the following major issues: definition of the cut path, primitive removal and re‐meshing, number of new primitives created, when re‐meshing is performed, and representation of the cutting tool. Many researches have developed schemes for interactive mesh cutting with the goals of reducing the number of new primitives created, creating new primitives with good aspect ratios, avoiding a disconnected mesh structure between primitives in the cut path, and representing the path traversed by the tool as accurately as possible. The goal of this paper is to explain how, by using a very simple framework, one can build a generalized cutting scheme. This method allows for any arbitrary cut to be made within a virtual object, and can simulate cutting surface, layered surface or tetrahedral objects using a virtual scalpel, scissors, or loop cautery tool. This method has been implemented in a real‐time, haptic‐rate surgical simulation system allowing arbitrary cuts to be made on high‐resolution patient‐specific models. Published in 2002 by John Wiley & Sons, Ltd.     

Multimedia group and inter-stream synchronization techniques: A comparative study

This paper presents the most comprehensive analysis and comparison of the most-known multimedia group and inter-stream synchronization approaches. Several types of multimedia synchronization are identified but only inter-stream and group synchronization algorithms are considered. This is the first survey including group synchronization techniques. A classification of the main synchronization techniques included in most of the analyzed algorithms complements the paper. Finally, a table is presented summarizing the main characteristics of each analyzed algorithm according to those techniques and other critical issues.     

Data-driven diagnosis of PEM fuel cell: A comparative study

This paper is dedicated to data-driven diagnosis for Polymer Electrolyte Membrane Fuel Cell (PEMFC). More precisely, it deals with water related faults (flooding and membrane drying) by using pattern classification methodologies. Firstly, a method based on physical considerations is defined to label the training data. Secondly, a feature extraction procedure is carried out to pick up the significant features from vectors constructed by individual cell voltages. Finally, a classification is adopted in the feature space to realize the fault diagnosis. Various feature extraction and classification methodologies are employed on a 20-cell PEMFC stack. The performances of these methodologies are compared.     

G1 rational blend interpolatory schemes: A comparative study

Interpolation of triangular meshes is a subject of great interest in many computer graphics related applications, as, for example, gaming and realtime rendering. One of the main approaches to interpolate the positions and normals of the mesh vertices is the use of parametric triangular Bézier patches. As it is well known, any method aiming at constructing a parametric, tangent plane (G¹) continuous surface has to deal with the vertex consistency problem. In this article, we propose a comparison of three methods appeared in the nineties that use a particular technique called rational blend to avoid this problem. Together with these three methods we present a new scheme, a cubic Gregory patch, that has been inspired by one of them. Our comparison includes an analysis of their computational costs on CPU and GPU, a study of their capabilities of approximating analytic surfaces and their response to different surface interrogation methods on arbitrary triangle meshes with a low triangle count that actually occur in their real-world use.     

Characteristics of active and passive dancers: A comparative study

A substantial number of web process lines use dancer mechanisms for attenuating web tension disturbances. Although passive dancer mechanisms are commonly used in web process lines, recently there has been a growing interest in active dancer mechanisms due to their ability to attenuate disturbances over a wide range of frequencies. The focus of the paper is on a comparative study of active and passive dancer mechanisms used in web processing machines for tension disturbance attenuation. Active and passive dancers are compared using simplified analytical models. To substantiate the analysis, results from experiments are shown and discussed.     

Constant round group key agreement protocols: A comparative study

The scope of this paper is to review and evaluate all constant round Group Key Agreement (GKA) protocols proposed so far in the literature. We have gathered all GKA protocols that require 1,2,3,4 and 5 rounds and examined their efficiency. In particular, we calculated each protocol’s computation and communication complexity and using proper assessments we compared their total energy cost. The evaluation of all protocols, interesting on its own, can also serve as a reference point for future works and contribute to the establishment of new, more efficient constant round protocols.     

Business analytics and business value: A comparative case study

With growing adoption of business analytics, it is important for investing firms to understand how business value is created from investments. Studies in IT domain have highlighted how higher investment in technology may not bring more returns, rather how IT as an organizational capability acts as a key mediator in value creation. This research extends the model to business analytics, to identify elements of analytics technology assets and business analytics capability and to understand the mechanism of business value creation using multiple case studies. We capture how analytics resources contribute to business performance by developing operational and organizational performance measures.     

遗传算法在多目标优化应用中的对比研究

多目标优化应用研究在过程工程领域越来越受重视。本文首先给出了多目标优化问题的一般形式,指出多目标问题求解任务：引导搜索向整个的Pareto优化范围;Pareto优化前沿上保持解集的多样性。在简要论述遗传算法求解多目标技术的基础上,对应用了遗传算法求解多目标的两种方法进行了对比研究,并给出了线性加权遗传算法和一种多目标遗传算法的计算框图。指出线性加权法求解Pareto最优解时不能不能很好地处理非凸区域、均匀分布的权重值不能生成均匀分布的Pareto前沿等局限性,以及多目标遗传算法生成种群多样性及Pareto最优解均匀分布的优点,并用实例进行了验证说明。     

Nonlinear controllers for solar thermal plants: A comparative study

Solar plants have nonlinear dynamics which must be taken into account when a control system is applied to them. The main purpose of the control systems is to maintain the outlet temperature in a desired reference value and, at the same time, attenuate the undesirable transients caused by the disturbances. Linear controllers, like PID ones, are not able to obtain good performance over the whole operation range of these kind of plants. To overcome these limitations two nonlinear controllers, a nonlinear model-based predictive controller and a distributed sliding mode controller, are applied to a solar plant in this work. The performance of these controllers is tested through experimental and simulation results, which show the tracking and disturbance rejection capabilities of the proposed controllers.     

Constraint scores for semi-supervised feature selection: A comparative study

Recent feature selection scores using pairwise constraints (must-link and cannot-link) have shown better performances than the unsupervised methods and comparable to the supervised ones. However, these scores use only the pairwise constraints and ignore the available information brought by the unlabeled data. Moreover, these constraint scores strongly depend on the given must-link and cannot-link subsets built by the user. In this paper, we address these problems and propose a new semi-supervised constraint score that uses both pairwise constraints and local properties of the unlabeled data. Experiments using Kendall’s coefficient and accuracy rates, show that this new score is less sensitive to the given constraints than the previous scores while providing similar performances.     

Practical fusion algorithms for rotation matrices: A comparative study

Many computer vision, sensor fusion, and robotic applications require the estimation of a 3 × 3 rotation matrix from a set of measured or computed 3 × 3 noisy rotation matrices. This article classifies solution methods into three categories: nonlinear least squares, linear optimal, and linear suboptimal algorithms. Their performance is compared through simulation studies. It is shown that the linear suboptimal algorithms proposed in this article have an accuracy comparable to that of the optimal algorithms and are about five times faster. Furthermore, a particular nonlinear optimization algorithm is presented that has computational complexity similar to that of the linear optimal procedures. © 1992 John Wiley & Sons, Inc.